Method of producing secondary aliphatic amines



Unitcd States Patent METHOD OF PRODUCING SECONDARY ALIIHATIC AMINES Sydney H. Shapiro, Chicago, Company, Chicago, 111.,

No Drawing. Application June 11, 1954, Serial No. 439,908

111., assignor to Armour and a corporation of Illinois This invention relates to a method of producing secondary aliphatic amines, which method has particular utility in producing unsaturated secondary aliphatic amines.

Both primary and secondary amines are prepared commercially by the hydrogenation of aliphatic nitriles over a hydrogenation catalyst. Raney nickel is the hydrogenation catalyst usually employed. It has been found to be feasible to produce both saturated and unsaturated primary aliphatic amines with hydrogenation catalysts such as Raney nickel, and these amine products are commercially available.

Saturated secondary aliphatic amines can also be readily prepared from aliphatic nitriles in the presence of hydrogenation catalysts like Raney nickel. However, unsaturated secondary aliphatic amines cannot be satisfactorily prepared by known hydrogenation processes from unsaturated aliphatic nitriles. While some slight degree of unsaturation can be retained in the product depending to some extent onthe degree of unsaturation of the starting material, the decrease in the degree of unsaturation during the formation of the secondary amines is such that the product must be sold as essentially saturated aliphatic amines. For example, an aliphatic nitrile starting material having an iodine value of 45 to 50 will result in a secondary amine product having an iodine value of 6 to 8 or less. For a product saleable as an unsaturated secondary amine product, the iodine value should be at least 30, and iodine values up to 75 or 80 for some applications would be desirable. Secondary unsaturated amine products having high iodine values would have uses and valuable properties different than and in addition to those of the corresponding saturated secondary amine product.

Another somewhat related problem is that the present hydrogenation processes for producing secondary amines do not provide a method for the direct production of these secondary amines, but instead primary amines are first produced as intermediates in the formation of the secondary amines. As pointed out by Homer Adkins in his book entitled, Reactions of Hydrogen With Organic Compounds Over Copper-Chromium Oxide and Nickel Catalysts (1937), at page 53, the formation of secondary amines during the hydrogenation of nitriles can be regarded as a side reaction, the formation of the secondary amines being due to interaction of an imine with primary amine. This reaction mechanism has certain disadvantages in regard to the rate of secondary amine formation and the yields of secondary amines obtained.

It is therefore a general object of this invention to provide a method for producing secondary amines substantially overcoming the problems discussed above. More specifically, it is an object of this invention to provide a commercially feasible method for producing unsaturated secondary aliphatic amines from unsaturated aliphatic nitriles. Still another object of this invention is to provide a method for the direct production of secondary amines from aliphatic nitriles without the necessity of forming primary amines as intermediates. Further objects and advantages will appear as the specification proceeds.

In one of its phases, this invention is concerned with a method of selectively producing secondary amines in which an aliphatic nitrile is hydrogenated in the presence of a copper-chromium oxide catalyst. In another of its phases, this invention is concerned with a'method of producing unsaturated secondary amines in which an alkylene nitrile is hydrogenated in the presence of a copper-chromium oxide catalyst while controlling the hydrogenation to selectively hydrogenate the nitrile groups to amine groups without hydrogenating the unsaturated carbon-to-carbon linkages. That this can be done is most surprising indeed, and is contrary to the accepted knowledge in this field.

Copper-chromium oxide or copper-chromite catalysts have been thought to selectively promote the hydrogenation of unsaturated linkages, and especially to do so in preference to other functional groups on the molecule, like cyanide or nitrile groups. For example, Homer Adkins and Ralph Connor, as reported in J. Am. Chem. Soc., 53, 1091-1095, reached the following conclusion:

An alkene linkage in a hydrocarbon as well as an acid or ketone may be hydrogenated without otherwise modifying the organic compound. The copper chromite catalyst is not active toward cyanides or towards benzenoid nuclei and thus offers a means for the selective hydrogenation of compounds containing these groups which are so readily reducible over nickel catalysts.

The prior thinking in regard to the preparation of amines from nitriles by hydrogenation, as represented by the above quotation, shows the unexpected nature of applicants invention. It is believed that no one skilled in the hydrogenation art prior to the present invention would have selected a copper-chromium oxide catalyst for the purpose of producing unsaturated secondary amines. The teaching of the prior art was diametrically against this, and suggests instead that a copper-chromium oxide catalyst might be used to selectively hydrogenate double bonds in a carbon chain without the reduction of functional groups attached to the chain such as cyanide or nitrile groups. It is probably for this reason that no effort was made to prepare either saturated or unsaturated secondary amines over copper-chromium oxide catalysts, although this type of catalyst is well known in the hydrogenation art and is employed for other purposes.

As indicated above, this application is based in part on the discovery that the use of a copper-chromium oxide catalyst for the hydrogenation of unsaturated aliphatic nitriles makes possible the preparation of the corresponding unsaturated secondary amine, a result which cannot satisfactorily be achieved with other hydrogenation catalysts like Raney nickel. The theoretical explanation for this result has not been developed, and as indicated above, does not seem to fit in with any accepted knowledge or theories in this field. However, the extensive experimental work leading to the present invention fully confirms this result, and some information has been obtained bearing on the reaction mechanism. Specifically, it has been shown that the formation of primary amines as intermediates is not necessary. In fact, it apparently does not occur to any appreciable extent with a copper-chromium oxide catalyst. In other words, the reaction is believed to take a diiferent course than the accepted reaction mechanism for the formation of secondary amines over Raney nickel and other hydrogenation catalysts. This makes possible the direct production of both saturated and unsaturated secondary amines, which is another aspect of applicants invention.

In practicing the present invention, commercially available copper-chromium oxide catalysts can be used. These catalysts are sometimes also referred to as copper- 3 chromite catalysts. Most commercially available copperchromite catalysts are stabilized with barium oxide, usually containing around 10% barium oxide, and these catalysts are suitable. However, it has been found that the presence of barium oxide is not important for the purposes of the present invention, and therefore it is preferred to employ copper-chromite catalysts which do not contain barium oxide or other stabilizing agents. Excellent results can be obtained with copper-chromite catalysts prepared as described by Calingaert and Edgar in the Journal of Industrial and Engineering Chemistry, vol. 26, p. 878. The ratio of copper to chromium oxide can be varied in the catalyst. This ratio is usually figured on the assumption that the copper is present as an oxide, the percent figures being given for the CuO content and the CraOa content. For the purposes of the present invention it is preferred to employ catalysts containing from 40 to 65% C110 and 35 to 60% CrzOs.

The amount of catalyst employed has not been found to be especially critical, and the percent catalyst in the reaction mixture can be varied over a rather wide range with good results, since the quantity of catalyst present seems to affect the rate rather than the course of the reaction or the nature of the final product obtained. For example, catalyst concentrations ranging from 1 to 5% by weight of the reaction mixture are satisfactory. It has been found that it is usually desirable to employ somewhat more of a fresh chromium oxide catalyst to achieve the same reaction rate than of a chromium oxide catalyst which has previously been used for producing secondary amines. In other words, the activity of the catalyst increases somewhat with reuse.

Any aliphatic nitrile or mixture of aliphatic nitriles can be used as the starting material. The nitriles prepared from the higher fatty acids in fats and oils are particularly suitable. This preferred class of aliphatic nitriles can be described as alkyl and alkylene nitriles containing from 8 to 22 carbon atoms. Mixtures of aliphatic nitriles prepared from natural mixtures of fatty acids are of particular importance because of the availability of such starting materials. These mixtures are usually identified by the fat or oil source, such as tallow nitriles, soya nitriles, etc.

In the preferred embodiment of the present invention unsaturated aliphatic nitriles are used as the starting material either alone or as part of a mixture containing both saturated and unsaturated nitriles, such as are found in tallow and soya nitriles. Tallow nitriles will usually have an iodine value of around 45 to 50, while other nitrile mixtures derived fromifats and oils containing larger amounts of unsaturated fatty acids, such as soya nitriles, will have higher iodine values. In the case of soya nitriles, an iodine value of 90 to 95 is typical. present process, such nitrile mixtures having iodine values of 35 and above can be hydrogenated with substantially no decrease in iodine value, as compared with prior art processes where the iodine value' drops to a very low figure. In general, 85 to 95% yields 'of unsaturated secondary aliphatic amines can be obtained with as little as 10% reduction in theinitial iodine value. The unsaturated secondary amine products thus produced have substantially lower melting points than the corresponding saturated secondary amine products and better solubility in organic solvents.

In general, the hydrogenation reaction can be carried out with the usual hydrogenation equipment and by the usual hydrogenation techniques for converting'aliphatic nitriles to amine. Temperatures of from 140 to 240 C. can be used, although a temperature range'frorn 150 to 215 C. is preferred. Similarly, pressures of from 100 to 1000 p. s. i. g. are feasible, although best results have been obtained with pressures ranging from 200 to 400 p. s. i. g. It is not necessary to employ a solvent in the reaction mixture, although an inert solvent can be used if desired.

By means of the Unsaturated aliphatic nitriles derived from naturallyoccurring fatty acids can contain from 14 to 22 carbon atoms, although the C18 unsaturated fatty acids predominate in animal and vegetable oils and fats. The common C18 unsaturated fatty acids are oleic, linoleic, and linolenic acids containing respectively from 1 to 3 un saturated bonds in the order stated. These acids can be separated from the saturated acids with which they are associated in natural fats and oils, and such separated unsaturated acids upon conversion to nitriles are useful starting materials for the present invention.

It has been found that the incorporation of a small amount of caustic in the reaction mixture suppresses tertiary amine formation, and this is an advantage in maximizing the yields of secondary amines. Any water-soluble inorganic hydroxide can be used as the caustic reagent, although the alkali metal hydroxides, particularly potassium and sodium hydroxides, are preferred.

' It has also been found that the unsaturated secondary amines produced by the method of this invention can be used to form quaternary ammonium compounds, and in particular di-alkene, di-methyl quaternary ammonium compounds. For example, the unsaturated secondary amine can be reacted with methyl chloride to produce the corresponding quaternary ammonium compound.

This invention is further illustrated by the following specific examples.

EXAMPLE I A copper-chromium oxide catalyst was prepared according to directions of Calingaert and Edgar in the Journal of Industrial & Engineering Chemistry, volume The specific procedure used was as follows:

250 g. of CuSO45H-2O and 149 g. of NaaCrzOvZHzO were dissolved in 1.2 liters of water. 28% aqueous ammonia was added (approximately cc.) until the supernatant liquid gave no further precipitation with a few drops of ammonia. The precipitate was filtered and washed until the wash waters were essentially free of color. At this time the precipitate was dried at C. and then ground to a powder. A portion of this powder was placed in a beaker in a sand bath and the temperature so adjusted that the temperature within the beaker did'not exceed 320 C. Heating was continued until decomposition was complete. The copper-chromium oxide catalyst prepared as described was bottled and stored to be used in the following experiments.

EXAMPLE II 500 g. of tallow nitrile (e. g., the mixture of nitriles prepared from tallow fatty acids), iodine value 48, 25 g. of copper-chromium oxide catalyst prepared as described in Example I, and 2 cc. of 20% NaOH were placed in a 3-liter autoclave equipped with an agitator. Autoclave was closed and flushed twice with 200 pounds hydrogen pressure. Then the heat and agitation were turned on, and the hydrogen pressure raised to 250 pounds. The temperature was maintained at 200 C. throughout the run. During the first three hours of reaction the unit was vented twice to zero pressure, then returned to 250 pounds pressure with hydrogen. During the next four hours the hydrogen pressure was raised to 800 pounds. At the end of this time the product analyzed as 79% secondary amine and 2% primary amine. The reaction was continued under the latter conditions for an additional five hours and then removed from the autoclave. The product analyzed was 89.5% secondary amine and less than 1% primary amine, with an iodine value of 40.1.

EXAMPLE I11 500 g. of tallow nitrile, iodine value 48, and 25 g. of copper chromite catalyst were placed in a.3-liter autoclave equipped with an agitator. The unit was closed and the system was flushed three times by raising the 75 pressure to pounds with hydrogen and then venting m racl s t the conclustion or this operation, the pressure'w'as raised to200 pounds with hydrogen and thegheat and agitator turned on.

The reaction was mainta ned at 200 C. for the remainder of the run and the pressure vented to zero at hourly interyal s At the end of six hours at temperature the product analyzed 84.1% secondary amine and 1.1% primary amine. At the end of thirteen hours, the product waswithdrawn from the autoclave and was analyzed as 82.8% secondary and 0.92% primary amine, with an iodine value of 47. I Q

" EXAMPLE IV 500 g. of tallow nitrile, iodine value 57,. and 25 g.;,o f copper-chromite catalyst were placed in a 3-liter autoclave equipped with an agitator. The unit was flushed three times withhydrogen as described in Example III. The unit was then closed, the pressure raised to 200 pounds-with hydrogen, and the agitator turned on. The

temperature was raised to 180 C. and maintained there during the entire run. The pressure was vented to zero once every hour. At the end of six hours the product contained 56% secondary and 2.1% primary amine. At the end of twelve hours the product was removed from the autoclave and was analyzed as 89.0% secondary and 0.79% primary amine with an iodine value of 41.2.

Iv EXAMPLE V This run was essentially a duplicate of Example IV, with the exception that the temperature was maintained at 160? C. throughout the experiment. The analysis of this run at various times is shown below:

XAMP j h runs were made using commerciallyfavailablei copper-chromite catalysts instead of the catalyst prepared as described in Example I. These commercial catalysts were stabilized with around 10% barium oxide. The tests were carried out in a manner similar to that described in the preceding examples. A reaction temperature of about 200 C. was used and no alkali was present. The results 7 of 4 runs are summarized below:

530 g. of nitrile from tallow fatty acids, acid value 0.75,

iodine value 51.2, and 15 g. of a commercial copperchromite catalyst were placed in a 3-liter autoclave equipped with a stirrer. The unit was closed and flushed three times with hydrogen and then the heat applied and the stirrer started.

The time, temperature and pressure conditions are shown below, as well as analyses at various stages:

Table I.-C0nditi0ns and analyses during the hydrogenation of tallow nitrile with copper-chromite catalyst EXAMPLE VI Percent Percent Time (hours) Secondary Primary Amine Amine Iodine value at 13 hours was 41.3.

EXAMPLE VII duplicate run of Example VI was made, with the single exception that the reaction was run at 210 C.

At the end of seven hours at temperature, the product was'93.6% secondary amine, 2.32% primary amine, with aniodine value of 39.5.

EXAMPLE VIII The catalyst filtered from the product of Example VII was added to 500 g. of tallow nitrile and 0.8 g. of NaOH in---a 3-liter autoclave. The unit was closed and flushed three times with hydrogen as previously described. The agitator was turned on and the temperature and pressure raised to 180' C. and 300 pounds hydrogen respectively. Atthe'end of 7 hours at temperature the product analyzed 94.5% secondary and 1.4% primary amine.

Time (hrs.)

Primary Total 1 A continuous vent of approximately 30 liters per hour of hydrogen was maintained during the entire run.

Final iodine value44.3.

EXAMPLE XI This experiment was a duplicate of Example X, with the single exception that 6 cc. of 2.5 N KOH was added to the charge. The time, temperature and pressure conditions and analyses at various stages of the run are shown below Table lI.C0na iti0ns and analyses during the hydrogenation of tallow nitrile with copper-chromite catalyst in the presence of small amounts of alkali Percent Amine Temp. Hydrogen 1 Time (hrs.) 0. Pressure,

lbs. Primary Second- Total ary 1 A continuous vent'oi approximately 30 liters of hydrogen per hour was maintained throughout the run.

Final iodine value-38.4.

EXAMPLE x11 A twenty-gallon autoclave was charged with '110 pounds of tallow nitrile, (iodine value 55.1) and 3.3 pounds of' a we??? Percent Amine Time (hrs) Primary Secondary Total Final iodine va1ue53.5.

EXAMPLE XIII This run was similar to run XII, except that 100 pounds of soya nitrile, iodine value 94.9, and 3 pounds of copperchromite catalyst were charged to the converter. The analyses at various stages of the reaction are shown below:

Percent Amine Time (hrs) Primary Secondary Total 3. s 0.1 0. 9 5. 4 17.2 22.6 7. 0 55. 5 03.1 0. 6 50. s 66.1 3. 0 60. 5 72. 5 1. 0 73. 0 75. 2 1. 2 s2. 8 s4. 0 0. a s4. 0 s4. 9 0.4 84. 6 85.0

Final iodine value-80.

EXAMPLE XIV This run was a duplicate of Example XIII, except that 80 pounds of soya nitrile and 2.4 pounds of copperchromite catalyst were charged to the reactor.

The analyses at various stages of the run follow.

alcohol were reacted with 33.7 pounds of methyl chloride as in Example XV. Final analysis was as follows:

Amine percent 1.17 5 Amine HCl do 0.13 Active do. 75 Product lbs 258 EXAMPLE XVII 10 1280 g. of technical n-dodecyl nitrile, acid value 0.66, 0.9 cc. of 30% NaOH and 37 g. of copper chromium oxide catalyst from Harshaw Chemical were placed in an autoclave. The unit was closed and flushed three times with 200# Hz.

Percent Amine Time (Hrs) Primary Secondary Total Percent Amine 4 'lime thrs.)

Primary Secondary Total Final iodine value-83.8.

EXAMPLE XV l pounds unsaturated, secondary amine derived from soya, 26 pounds of NaHCOs, and 33 pounds of alcohol 60 were charged into a gallon autoclave. The reactor was closed and 28 pounds of methyl chloride was added gradually into the unit at from 75-120 pounds p. s. i. g. and the reaction mixture was agitated and heated to from to 200 F. until reaction was complete. ()9

The final analysis was as follows:

Amine percent 1.04 Amine HCl d0 0.28 Active c do 75.0 7 Product lbs 212 EXAMPLE XVI pounds of unsaturated secondary amine derived from tallow, 24 pounds of NaHCOs, and 54 pounds of 75 While in the foregoing specification this invention has been described in relation to certain specific embodiments thereof and many details have been set .forth in connection with these embodiments, it will be apparent to those skilled in the art that the invention is susceptible to other embodiments and that many of the details set forth can be varied considerably without departing from the basic concepts of the invention.

I claim:

1. The method of preparing secondary amines from nitriles, comprising contacting the nitrile reactant with hydrogen in the presence of a copper-chromium oxide hydrogenation catalyst at hydrogenation temperatures and pressures, said nitrile reactant being selected from the group consisting of alkene nitriles, alkane nitriles, and mixtures of alkane and alkene nitriles, said catalyst containing substantial amounts of both copper and chromium oxide, and continuing said contacting until a substantial portion of said nitrile reactant is converted to secondary amines.

2. The method of preparing secondary amines, comprising contacting a mixture of alkane and alkene nitriles with hydrogen in the presence of a copper-chromium oxide hydrogenation catalyst at hydrogenation temperatures and pressures, the nitriles in said mixture being ones which can be converted to aliphatic amines by hydrogenation, said catalyst containing substantial amounts of both copper and chromium oxide, and continuing said contacting until a substantial portion of said nitrile mixture is converted to secondary amines.

3. The method of claim 2 in which said catalyst contains from 35 to 60% chromium oxide on a CrzOs basis and from 40 to 65% copper on a CuO basis.

4. The method of preparing secondary amines containing alkene groups, comprising contacting an alkene nitrile containing from 14 to 22 carbon atoms with hydrogen in the presence of a copper-chromium oxide hydrogenation catalyst at hydrogenation temperatures and pressures, said catalyst containing a substantial amount of both copper and chromium oxide, and continuing said contacting until a substantial portion of said alkene nitrile is converted to secondary amines containing alkene groups.

5. The method of claim 4 in which said catalyst contains from 35 to 60% chromium oxide on a CrzOs basis and from 40 to 65% copper on a CuO basis.

6. The method of claim 4 in which said contacting is also carried out in the presence of a sufiicient amount of a water-soluble inorganic alkali to suppress tertiary amine formation.

9 10 7. The method of preparing secondary amines con- 8. The method of claim 7 in which said catalyst containing alkene groups, comprising contacting with hytains from 35 to 60% chromium oxide on a CrzOa basis drogen a mixture of alkane and alkene nitriles in the and from 40 to 60% copper on a CuO basis. presence of a copper-chromium oxide hydrogenation catalyst at hydrogenation temperatures and pressures, said 5 References Cited in the file of this patent mixture having an iodine value of at least 35, said catalyst containing substantial amounts of both copper and UNITED STATES PATENTS chromium oxide, and continuing said contacting until a 2,355,356 Young Aug. 8, 1944 major portion of said mixture is converted to a secondary 2,436,368 Weber et a1. Feb. 17, 1948 amine product having an iodine value generally corre- 10 2,449,036 Grunfeld Sept. 7, 1948 spending to that of said mixture. 

1. THE METHOD OF PREPARING SECONDARY AMINES FROM NITRILES, COMPRISING CONTACTING THE NITRILE REACTANT WITH HYDROGEN IN THE PRESENCE OF A COPPER-CHROMIUM OXIDE HYDROGENATION CATALYST AT HYDROGENATION TEMPERATURES AND PRESSURES, SAID NITRILE REACTANT BEING SELECTED FROM THE GROUP CONSISTING OF ALKENE NITRILES, ALKANE NITRILES, AND MIXTURES OF ALKANE AND ALKENE NITRILE, SAID CATALYST CONTAINING SUBSTANTIAL AMOUNTS OF BOTH COPPER AND CHROMIUM OXIDE, AND CONTINUING SAID CONTACTING UNTIL A SUBSTANTIAL PORTION OF SAID NITRILE REACTANT IS CONVERTED TO SECONDARY AMINES. 